Replacing Thetford N150 Fridge Heater Elements

Posted on by David Burley

Conducting a habitation service on a customers van today and the customer had pre warned us of a fault on their Thetford N150 Refrigerator whereby everything was ok on Gas and 12v but if he selected 230v then the spanner symbol appeared on the small LCD Panel and a Number 1.

Thetford Error codes for the N150 are shown below:-

Refrigerators with a LCD control panel have a special diagnostics area which
displays an error code if there is a fault.
• Fault 1: AC heater current is measured to be 75% below nominal current.
• Fault 2: DC heater current is measured to be 75% below nominal current.
• Fault 3: AC heater is ON when it should be OFF.
• Fault 4: DC heater is ON when it should be OFF.
• Fault 5: Senses flame when gas should be OFF.
• Fault 6: Senses gas output terminal ON when should be OFF.
• Fault 7: Senses gas output terminal OFF when should be ON.
• Fault 8: AC mains supply is 20% below nominal.
• Fault 9: Gas lockout because flame fails to ignite after 30 seconds.
• Fault 10: No “engine running” signal is present and control is in Manual DC mode.
• Fault 11: No energy source is available and control is in AUTO mode.
• Fault 12: Contact your dealer or a Thetford Service Centre.
• Fault 13: Thermistor fails; control automatically switches to Backup mode (BOS).
• Fault 14: Display Board and Power board lost communication with each other.
• Fault 18: No fault, only lighting all LCD segments on start-up.

So in this case it was indicating a problem with the AC Heater Element, a few checks of 230v Supply available and then dismantling the power board housing to check the 5A Glass fuse pointed us in the direction of the Element. Putting a multimeter across the connections for the element showed open circuit. So we knew the problem but extracting the old element wasn’t quite as easy.

You can either disconnect all supply cables (12v / 230v) and the Gas connections. Open the fridge / freezer doors and unscrew the fridge from its housing and then withdraw the fridge slowly with someone on the other side sighting everything is ok, or alternatively this particular fridge has a small side plate opening on the flue allowing easier access to the elements. The 12v one is behind the 230v one.

With small fingers and lots of patience and wiggling of the element it can be withdrawn vertically (It is easier to first withdraw the 12v one somewhat to give better access otherwise the 230v element rubs against it causing friction and making it even more difficult to extract.

Finally the offending item is removed as below.

Thetford N150 fridge Heater Element








Update 16/01/2014

The replacement heater element arrived this morning, we immediately tested it to ensure it was ok prior to fitting and as can be seen below the resistance reading we got was ideally between the manufacturers parameters (between 218 -> 266 Ohms)

Much easier to install the new heater element than it was to remove the old one and note from the images the difference on the old heater vs new with the colour / corrosion levels. (The image on the left is the new element)

Once the element was installed, the power box was reassembled and the whole system gas tested and the fridge tested on AC all ok.

Back to the customer

new element for dometic n150 fridgedometic n150 fridge heater element open circuit









About David Burley


David lives & breathes motorhomes, an ex Fulltimer who has years of experience living in a motorhome and now drawing on his Royal Navy Technical engineering background for installation work.

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